Terephthalate (also known as terephthalic acid and PTA) is the immediate precursor of polyethylene terephthalate (PET), used to make clothing, resins, plastic bottles and even as a poultry feed additive. Nearly all PTA is produced from para-xylene by oxidation in air in a process known as the Mid Century Process. This oxidation is conducted at high temperature in an acetic acid solvent with a catalyst composed of cobalt and/or manganese salts. Para-xylene is derived from petrochemical sources and is formed by high severity catalytic reforming of naphtha. Xylene is also obtained from the pyrolysis gasoline stream in a naphtha steam cracker and by toluene disproportion.
Cost-effective methods for generating renewable PTA have not yet been developed to date. PTA, toluene and other aromatic precursors are naturally degraded by some bacteria. However, these degradation pathways typically involve monooxygenases that operate irreversibly in the degradative direction. Hence, biosynthetic pathways for PTA are severely limited by the properties of known enzymes to date.
A promising precursor for PTA is p-toluate, also known as p-methylbenzoate. P-Toluate is an intermediate in some industrial processes for the oxidation of p-xylene to PTA. It is also an intermediate for polymer stabilizers, pesticides, light sensitive compounds, animal feed supplements and other organic chemicals. Only slightly soluble in aqueous solution, p-toluate is a solid at physiological temperatures, with a melting point of 275° C. Microbial catalysts for synthesizing this compound from sugar feedstocks have not been described to date.
Petrochemical based chemical syntheses for making terephthalic acid are known (see, e.g., U.S. Pat. Nos. 2,905,709; 3,023,234; 3,042,717; 3,043,846; 3,064,041; 3,096,366; and 6,441,225). Alternative technologies for the production of terephthalic acid have been made feasible with the advent of molecular recombinant technologies used to modify biosynthetic pathways in microbial organisms. For example, microbial organisms have been described which produce precursors useful for the synthesis of bio-based terephthalic acid. Exemplary indirect semi-synthetic routes of producing bio-based terephthalic acid are described in U.S. Patent Publication No. 2011/0124911 A1. Direct biosynthetic routes, wherein terephthalate is itself biosynthesized in microbial organisms have been described in U.S. Patent Publication No. 2011/0207185 A1. Even with advantages that bio-based production of terephthalic acid offers, improvements and/or additional processes are sought, for example, to improve recovery of terephthalic acid in terms of yields and purity, and to increase efficiency and scalability of the processes including, for instance, reducing the number of manufacturing steps, lowering energy usage, recapturing and recycling materials and reducing environmental discharges.
Thus, there exists a need for alternative methods for effectively producing and isolating commercial quantities of compounds such as p-toluate or terephthalate. The present invention satisfies this need and provides related advantages as well.